Participants from four Chinese regions have been barred from attending the Asian Youth Day - Asia's version of the World Youth Day - under way in Hong Kong this week.

The Bangkok Post reports that six hundred people including Hong Kong's Beijing-appointed leader Donald Tsang were due to attend the opening ceremony of week-long Asian Youth Day event.

However, Hong Kong cardinal Joseph Zen told a Chinese newspaper that Catholics from four mainland regions had been told they could not attend because it was seen as an "anti-China" event.

"A lot of people told us they would like to come but they have not been able to get special permission on the mainland to attend the event," Cardinal Zen told the newspaper, without naming the regions.

"It is very sad that officials have ruined this opportunity for exchange, even though this is a spiritual and not a political event."

Sixty Catholics from mainland China will join the event, fewer than the Cardinal said he and other organisers of the event had been hoping for.

The incident follows tensions between the Vatican and Beijing over the ordination of unauthorised Catholic bishops in China earlier this year.

China allows Catholics to worship but only through the officially controlled church, which operates outside of the Vatican's sphere.

Diplomatic relations between the Vatican and Beijing were severed in 1951 because of the Vatican's decision to recognise Taiwan, which China regards as a renegade province.

Talks have been under way in recent months to restore diplomatic ties although the talks received a setback with the unauthorised ordinations of bishops in China.